1. Field
The present disclosure relates to a developing device that is used in an image forming apparatus such as a copier, a multifunctional printer, a printer, a facsimile apparatus and an image forming apparatus including the developing device.
2. Description of the Related Art
An image forming apparatus such as a copier, a multifunctional printer, a printer, a facsimile apparatus is configured to, for example, in electrophotographically forming an image, charge a surface of an electrostatic latent image support such as a photoreceptor, form an electrostatic latent image by performing image exposure in the charged region, visualize (develop) the electrostatic latent image as a toner image, transfer the toner image thus visualized onto an intermediate transfer body such as an intermediate transfer belt or a recording material such as a sheet of paper, further transferring the toner image onto the recording material when having transferred the toner image onto the intermediate transfer body, and fixing the toner image to the recording material onto which the toner image has been transferred.
In general, a developing device that is used in such an image forming apparatus includes a magnet roller, a developing sleeve that revolves in a predetermined direction of revolution around the magnet roller, a developer tank having an opening that forms a development region by opening a part of a surface of the developing sleeve in a circumferential direction, and a regulating member that regulates a layer thickness of a developer on the surface of the developing sleeve. Note here that possible examples of the developer include a two-component developer (i.e. a developer composed mainly of a toner and a carrier) and a magnetic single-component developer (i.e. a developer composed mainly of a magnetic toner). Further, in using the developer to develop the electrostatic latent image formed on the electrostatic latent image support, a developing bias voltage is applied between the developing sleeve and the electrostatic latent image support.
Depending on the composition of the developer (in the case of the two-component developer, the toner and/or the carrier, or in the case of the magnetic single-component developer, the magnetic toner), the state of external additives, and/or the properties (e.g. surface material and/or surface treatment) of the surface of the developing sleeve, such a developing device may suffer from a residue of the toner adhering directly to the surface of the developing sleeve due to forces of adhesion such as van der Waals forces, although the toner is supposed to be released from the surface of the developing sleeve by centrifugal force generated by the revolution of the developing sleeve after the end of a developing process of developing the electrostatic latent image being supported the electrostatic latent image support. The residue of the toner adhering directly to the surface of the developing sleeve remains with charge generated by the previous image and therefore differs in amount of charge from a portion of the toner newly drawn up onto the surface of the developing sleeve by the next revolution, thus inconveniently affecting the next image to be developed.
Furthermore, while the developer on the surface of the developing sleeve is supposed to be replaced with a new developer every time the developing sleeve revolves, a portion of the toner remains (stays) in the same place on the surface of the developing sleeve, and depending on the direction in which the developing bias voltage is applied, the toner is pressed against the surface of the developing sleeve, with the result than the toner may adhere firmly no the surface of the developing sleeve. Then, the layer of the toner having adhered to the surface of the developing sleeve weakens the magnetic force of the magnet roller, lowers the amount of the developer that is conveyed on the surface of the developing sleeve, and by extension inconveniently invites shortening of the life of the developing sleeve.
It is conceivable that such inconveniences may be obviated, for example, by repeating experiments with slight variations in the composition of the developer (in the case of the two-component developer, the toner and/or the carrier, or in the case of the magnetic single-component developer, the magnetic toner), the state of external additives, and/or the properties (e.g. surface material and/or surface treatment) of the surface of the developing sleeve and thereby finding out such a combination of the composition of the developer, the state of external additives, and/or the properties of the surface of the developing sleeve as to reduce a residue of the toner adhering directly to the surface of the developing sleeve. In this case, however, an enormous number of experiments need to be conducted, thus entailing much labor.
To address this problem, Japanese Unexamined Patent Application Publication No. 2014-215403 discloses specifying the particle diameter of the toner and the average degree of circularity of the toner and thereby reducing a residue of the toner adhering directly to the surface of the developing sleeve.
However, the method disclosed in Japanese Unexamined Patent Application Publication No. 2014-215403 is limited in scope of toner to be used and is high in cost of usage of toner.